1. Field of the Invention
The present invention relates to a signal processing apparatus, and more particularly, to an audio reproducing apparatus.
2. Description of the Related Art
A so-called minicomponent, a flat-screen television, or the like tends to have a speaker with a small diameter and a speaker box (enclosure) with a small capacity in which the speaker is placed. Accordingly, the resonance frequency f0 of the speaker is about 100 Hz or higher in many cases.
Generally, when an audio signal whose frequency is lower than or equal to the resonance frequency f0 of a speaker is supplied to the speaker, as the frequency of the audio signal increases, the sound pressure of the fundamental frequency component decreases, and the number of frequency components (harmonic components) that cause sound distortion rapidly increases.
Thus, it is difficult for an audio reproducing apparatus in which the above-mentioned speaker having a small diameter is used to sufficiently reproduce bass whose frequency is lower than or equal to the resonance frequency f0 of the speaker.
An instrumental tone includes the fundamental and its harmonics, and the tone color is decided by the ratio between the fundamental and its harmonics. Regarding audibility, even when the fundamental is not output, the output of its harmonics enables a listener to perceive the output sound as if the fundamental were output. This is psychoacoustically verified.
An audio reproducing apparatus allowing a listener to experience bass using such a sensory property has been suggested. FIG. 11 is a flow diagram of an exemplary audio reproducing apparatus using the sensory property. The exemplary audio processing apparatus includes a speaker 5 having a small diameter whose bass is to be experienced by a listener should be improved.
An audio signal S1 is supplied through an input terminal 1 to a high-pass filter 2. As shown in part (A) of FIG. 12, high and midrange frequency components S2 whose frequencies are higher than or equal to the resonance frequency f0 of the speaker 5 are extracted from the audio signal S1 in the high-pass filter 2 and supplied to a combining circuit 3. Additionally, the audio signal S1 is supplied through the input terminal 1 to a band-pass filter 7. As shown in part (B) of FIG. 12, low frequency components S7 whose frequencies are from f0/2 to f0 are extracted from the audio signal S1 in the band-pass filter 7 and supplied to a pitch shifter 8.
The pitch shifter 8 multiplies the frequencies of the low frequency components S7 supplied thereto by two. As shown in part (C) of FIG. 12, harmonic components S8 whose frequencies are from f0 to 2f0 are output from the pitch shifter 8.
The harmonic components S8 are supplied to the combining circuit 3 to be combined with the high and midrange frequency components S2, and the combining circuit 3 outputs an audio signal S3 including the intensified harmonic components S8 of the low frequency components S7, as shown in part (D) of FIG. 12. This audio signal S3 is supplied through a power amplifier 4 to the speaker 5. Accordingly, a sound having the frequency characteristic shown in part (D) of FIG. 12, i.e., a sound of the audio signal S3 including the intensified harmonic components S8 of the low frequency components S7, is output from the speaker 5.
In this case, the speaker 5 does not output the sound of the low frequency components S7 but outputs the sound of the harmonic components S8 whose fundamental frequency components are the low frequency components S7. As described above, this allows the listener to perceive the sound as if the sound of the low frequency components S7 were output. Thus, the listener can experience the bass although the speaker 5 has a small diameter.
It is regarded that in a case where the frequencies of the harmonic components S7 are multiplied by an integer to generate the harmonic components S8, when the frequencies of the low frequency components S8 are about 200 Hz or lower, the sound of the harmonic components S8 does not make the listener feel that there is something wrong with the sound.
Japanese Unexamined Patent Application Publication No. 8-213862 is given as the related art document.